family

Asteraceae

status

Senegal tea plant (Gymnocoronis spilanthoides) is listed as noxious in class 1 throughout NSW, meaning the Local Control Authority (usually Council) must be notified immediately if an infestation is discovered, the plant must be eradicated and the site kept free of the weed. It cannot be sold or propagated or knowingly distributed. Senegal tea plant is on the federal government alert list of 28 environmental weeds which currently have a limited Australian distribution but show considerable weed potential. The complete eradication of these species from Australia is highly desirable.

description

Senegal tea plant is an emergent perennial herb growing in shallow water or on mud around the water’s edge. It may form rounded clumps of stems, or a tangled mass of stems spreading across mud. It spreads by rhizomes (underground runners). Stems are pale green to reddish at the base, erect or prostrate, branching at the nodes, and up to 1.5 metres long and 10-15mm diameter, cane-like and hollow between the joints. Leaves are lance-shaped to oval, dark green, on short stalks, with the margins serrated and slightly wavy. Flowers are small and white to mauve, in dense hemispherical clusters 1-2 cm across at the stem tips, enclosed before opening in a single row of green bracts. The first 3 photos above are of this weed (photos provided by Sheldon Navie of the University of Queensland).

preferred habitat and impacts

Still or very slowly flowing fresh water in tropical to warm-temperate climate is the preferred habitat. Introduced from tropical America for the aquarium trade and naturalised in a few widely separated areas, including the NSW north coast and Illawarra.Senegal tea plant could blanket the water surface reducing light levels, temperature and oxygen in the water below. This has profound effects on communities of native plants and animals in the water. It may interfere with animal access for drinking water, human access for swimming and boating, reduce water quality and block pumps.

dispersal

Dumping of aquarium or ornamental pond plants is often the means of spread for aquatic weeds. The record from the Illawarra was of plants deliberately cultivated in a farm dam to provide stock for the aquarium trade.

look-alikes

Senegal tea should be easily recognised when in flower, as the white flowers on an aquatic plant are distinctive. Prior to flowering the plants could be confused with a number of native and exotic species which grow in or near water. The weed, blue water speedwell (Veronica anagallis-aquatica) has hollow stems, an erect habit and rhizomes. Its leaves are opposite and finely toothed, but are stalkless (senegal tea leaves are on short stalks). Water speedwell flowers are pale blue or mauve and arranged in long terminal spikes with large gaps between flowers.

Alligator weed (Alternanthera philoxeroides) is an aquatic weed with a sprawling habit which can also grow on dry land around the edge of water bodies. Its leaves are blunt-tipped and lack marginal teeth, and are in opposite pairs. Flowers are small and white, a little similar to those of Senegal tea plant, but are held in small clusters on a short stalk in the axil of each leaf, not in terminal clusters.

The native plant square raspwort (Haloragis exalata ssp exalata) forms similar clumps of erect stems which are red at the base and green above, and it has opposite leaves with toothed edges. However, the most common form of this plant, variety exalata, has raspy textured stems and leaves, covered with small stiff hairs. A very rare form, var laevis, has smooth, glossy leaves and stems. The stems are not hollow. The flowers of this plant are tiny and look more like buds, in terminal spikes or in the upper leaf axils. It grows around the edges of coastal lakes, often in brackish or saline situations, and may also occur in freshwater situations such as on creek banks. It generally grows above the water level, but may be inundated during flooding.

Crofton weed (Ageratina adenophora), also in the daisy family, has white flowers similar to those of Senegal tea plant, but its leaves are shorter and more triangular in shape and are on long stalks. Stems are not hollow. It grows in damp places but it is not aquatic.

control

Most importantly, do not dump unwanted aquatic plants into water bodies, or grow species with weed potential in ornamental ponds or aquaria. Some invasive water plants are still sometimes sold by nurseries or pet shops. If you notice this, report the instance to Council, so that the proprietors can be advised that it is illegal to sell these plants.Once an infestation is established, and has been definitely identified, there are two options, mechanical or chemical control. Plants can be raked to shore and piled on the shore above flood reach under plastic, where they will break down. Vigilance will be needed to ensure that plants do not recover. For large infestations herbicide may be necessary, but a permit will be required from the Environmental Protection Agency to apply any herbicide to a water body. Only a limited number of herbicides are registered for use over water. If you suspect you have an outbreak of an aquatic weed, notify your local weed control authority (usually Council) and take their advice on control methods.